Is it possible to run hot cathode fluorescent lamps in cold cathode mode? Iwant to build a portable UV lamp that runs off 6V, and want to use 2 9 wattpreheat germicidal lamps in cold cathode mode (to simplify the ballast design).

Is it possible to run hot cathode fluorescent lamps in cold cathode mode?=Iwant to build a portable UV lamp that runs off 6V, and want to use 2 9 =wattpreheat germicidal lamps in cold cathode mode (to simplify the ballast =design).Any suggestions?

There are two aspectso Striking it in cold cathode modeo Running it in cold cathode mode

Running in cold cathode mode means under-running the tube so that thetube current is significantly lower than designed and hence the tubevoltage is higher than designed for and the electrodes don't heat upto thermionic operating temperature. This results in higher energyelectrons and ions impacting on the electrodes, and will sputter offthe thermionic emission coating - this doesn't matter much as youaren't using the coating when running in cold cathode mode, but itwill generate dark shadows inside the glass at the tube ends. The lightintensity will be much less, but the energy spectrum will move towardsthe higher frequency (higher energy) UV bands.

If you intend to start the tube in cold cathode mode but then run itat full power (which will change to thermonic emission mode within asecond or two), the cold cathode starting will wear the thermionicemission coating which is required to run the tube, so you will getfewer tube starts out of it. This won't matter if the tube operatesfor many hours each switch-on, but would give you a shorter tube lifeif the tube only operates for a short time with lots of switch-ons.

One other thing to watchout for is that if your control gear canprovide enough over voltage to keep the tube running at more thanfull power after the emission coating is all sputtered off (whichis really a dead tube), the electrode ends can change to run incold cathode mode, which at full tube current will make the tubeends very hot, and can cause the glass to melt or crack, and canignite any nearby inflamable materials. Electronic ballasts usuallytry to detect when the thermionic emission coating finally wears offand stop driving the tube, to prevent this happening. One end willalways wear out before the other, and this causes the tube to partiallyrectify (different voltage drop in each direction), and this is usedto detect that the tube is end-of-life and stop driving it before itoverheats.

--Andrew Gabriel[email address is not usable -- followup in the newsgroup]

Is it possible to run hot cathode fluorescent lamps in cold cathode mode?=Iwant to build a portable UV lamp that runs off 6V, and want to use 2 9 =wattpreheat germicidal lamps in cold cathode mode (to simplify the ballast =design).Any suggestions?

There are two aspectso Striking it in cold cathode modeo Running it in cold cathode modeRunning in cold cathode mode means under-running the tube so that thetube current is significantly lower than designed and hence the tubevoltage is higher than designed for and the electrodes don't heat upto thermionic operating temperature. This results in higher energyelectrons and ions impacting on the electrodes, and will sputter offthe thermionic emission coating - this doesn't matter much as youaren't using the coating when running in cold cathode mode, but itwill generate dark shadows inside the glass at the tube ends. The lightintensity will be much less, but the energy spectrum will move towardsthe higher frequency (higher energy) UV bands.If you intend to start the tube in cold cathode mode but then run itat full power (which will change to thermonic emission mode within asecond or two), the cold cathode starting will wear the thermionicemission coating which is required to run the tube, so you will getfewer tube starts out of it. This won't matter if the tube operatesfor many hours each switch-on, but would give you a shorter tube lifeif the tube only operates for a short time with lots of switch-ons.One other thing to watchout for is that if your control gear canprovide enough over voltage to keep the tube running at more thanfull power after the emission coating is all sputtered off (whichis really a dead tube), the electrode ends can change to run incold cathode mode, which at full tube current will make the tubeends very hot, and can cause the glass to melt or crack, and canignite any nearby inflamable materials. Electronic ballasts usuallytry to detect when the thermionic emission coating finally wears offand stop driving the tube, to prevent this happening. One end willalways wear out before the other, and this causes the tube to partiallyrectify (different voltage drop in each direction), and this is usedto detect that the tube is end-of-life and stop driving it before itoverheats.

Thanks for your advice.

Do you have any suggestions as to where I could find a decent schematic for a6V ballast to run one of these tubes in hot cathode mode? There are a fewschematics out there, but all require an unspecified special transformer.

I would run the device for short periods so as not to drain the batteries. Ican run two ballasts to work both tubes.

Do you have any suggestions as to where I could find a decent schematic =for a6V ballast to run one of these tubes in hot cathode mode? There are a =fewschematics out there, but all require an unspecified special transformer.I would run the device for short periods so as not to drain the =batteries. Ican run two ballasts to work both tubes.

I would look for a low voltage compact fluorescent lamp of similarpower rating, and extract the electronic ballast from that.I haven't seen 6V compact fluorescents, but 12V ones have beenavailable, although I would expect them to give way to LEDs ifthey haven't already.

Some notes on reusing compact fluorescent integral control gearhere: http://www.cucumber.demon.co.uk/lights/diy/

--Andrew Gabriel[email address is not usable -- followup in the newsgroup]

Post by SteveDo you have any suggestions as to where I could find a decentschematic for a 6V ballast to run one of these tubes in hot cathodemode? There are a few schematics out there, but all require anunspecified special transformer.

There are some at http://www.repairfaq.org/sam/samschem.htm#schinv .Many of them give the mechanical specifications for winding thetransformer; a few of them use "standard" 120 V power transformers.

Post by SteveIs it possible to run hot cathode fluorescent lamps in cold cathode mode? Iwant to build a portable UV lamp that runs off 6V, and want to use 2 9 wattpreheat germicidal lamps in cold cathode mode (to simplify the ballast design).Any suggestions?

No. Cold cathode fluorescent lamps have large area electrodes so thecurrent density is very low. You can, however, run the lamp inInstant Start mode.--Vic Robertshttp://www.RobertsResearchInc.comhttp://www.cflfacts.comsci.engr.lighting Rogues Gallery http://www.langmuir.orgTo reply via e-mail:replace xyz with vdr in the Reply to: addressor use e-mail address listed at the Web site.

This information is provided for educational purposes only.It may not be used in any publication or posted on any Website without written permission.